Cr(VI) salts, particularly the insoluble compounds, are well-established human carcinogens, affecting the bronchial cells of the lung. No investigations have studied particulate Cr(VI) and only one has studied soluble Cr(VI) in human bronchial cells. Thus the goal of this research is to understand the mechanisms of Cr(VI)-induced carcinogenesis in human bronchial cells. The general hypothesis guiding this proposal is that particulate Cr(VI) is a more potent carcinogen than soluble Cr(VI) because it can escape cell cycle arrest at genotoxic doses. The specific goal of this project is to establish a human bronchial cell model to investigate these mechanisms. Three hypotheses will be tested: 1) Cr(VI) is genotoxic in human bronchial cells. 2) Particulate Cr(VI) compounds are more potent carcinogens than soluble Cr(VI) compounds because they provide chronic extracellular Cr(VI) exposure and escape cell cycle delay. 3) Particulate Cr(VI) salts escape cell cycle delay because of their divalent counter ion. These hypotheses will be tested with the following: 1) Cr(VI)-induced genotoxicity will be measured by the amount of damage produced in the Comet assay, and in metaphase chromosome spreads. Results will provide the first data on the carcinogenic and genotoxic effects of intact Cr(VI) particles to its target cells. 2) Particle uptake will be measured with transmission electron microscopy and ion uptake will be measured with inductively coupled plasma mass spectrometry. 3). Cell cycle effects will be measured with a mitotic index, fluorescent automated cell sorting and cDNA expression arrays. Results will the first reports of Cr(VI) toxicity in its target cells, the first detailed information of the interaction of Cr(VI) with the cell cycle, and will provide important toxicological data on the differences between particulate and soluble hexavalent chromium. This research is significant because it will provide: 1) an understanding of how Cr(VI) causes genetic in its target cells; 2) essential information to better assess the relative risk of exposure to particulate or soluble Cr(VI); 3) models of human bronchial cells for further study of Cr(VI), other metals, and lung cancer in general.